Effect of melt compounding temperature on dielectric relaxation and ionic conduction in PEO–NaClO4–MMT nanocomposite electrolytes

Abstract

Polymer nanocomposite electrolytes (PNCEs) of poly(ethylene oxide) and sodium perchlorate monohydrate complexes with montmorillonite (MMT) clay up to 20 wt. % MMT concentration of poly(ethylene oxide) (PEO) are synthesized by melt compounding technique at melting temperature of PEO (∼70°C) and NaClO 4 monohydrate (∼140°C). Complex dielectric function, electric modulus, alternating current (ac) electrical conductivity, and impedance properties of these PNCEs films are investigated in the frequency range 20 Hz to 1 MHz at ambient temperature. The direct current conductivity of these materials was determined by fitting the frequency-dependent ac conductivity spectra to the Jonscher power law. The PNCEs films synthesized at melting temperature of NaClO 4 monohydrate have conductivity values lower than that of synthesized at PEO melting temperature. The complex impedance plane plots of these PNCEs films have a semicircular arc in upper frequency region corresponding to the bulk material properties and are followed by a spike in the lower frequency range owing to the electrode polarization phenomena. Relaxation times of electrode polarization and ionic conduction relaxation processes are determined from the frequency values corresponding to peaks in loss tangent and electric modulus loss spectra, respectively. A correlation is observed between the ionic conductivity and dielectric relaxation processes in the investigated PNCEs materials of varying MMT clay concentration. The scaled ac conductivity spectra of these PNCEs materials also obey the ac universality law.

Dielectric spectroscopy and confirmation of ion conduction mechanism in direct melt compounded hot-press polymer nanocomposite electrolytes

“…2. These spectra have peaks in the frequency range 10 3 to 10 4 Hz, which correspond to the electrode polarization relaxation frequency, f EP [11,[18][19][20][21]31]. The f EP separates the bulk material properties from the contribution of EP process, which occurs in the lower-frequency region due to formation of electric double layers (EDLs) (also known as blocking layers) by the free charges that build up at Insets show the enlarged view at high frequencies and also the variation of ε′ at 1 MHz with weight percent MMT concentration interface between the dielectric material and the metallic electrode surfaces in plane geometry [18,31].…”

“…This observation confirms the suitability of both tanδ and σ′ spectra of PNCE materials for the characterization and analysis of the EP phenomena affected frequency region. The electrode polarization relaxation time C EP , which involves charging and discharging time of the EDLs capacitances, is determined by the relation t EP ¼ 2pf EP ð Þ À1 [11,34]. The evaluated C EP values of the PNCE films are recorded in Table 1 which vary anomalously with the increase of MMT concentration.…”

“…The details of the evaluation of intensive quantities, namely complex dielectric function " » w ð Þ ¼ " 0 À j" 00 , complex ac electrical conductivity s » w ð Þ ¼ s 0 þ js 00 , and complex electric modulus M » w ð Þ ¼ M 0 þ jM 00 and extensive quantity, i.e. complex impedance Z » w ð Þ ¼ Z 0 À jZ 00 of the films, are described by us elsewhere [11,22,25,26].…”

“…During the last decade, synthesization of poly(ethylene oxide) (PEO) and alkaline metal salt-based solid-type polymer nanocomposite electrolyte (PNCE) of improved mechanical, thermal and electrochemical stability with enhanced ionic conductivity has received extensive attention as candidate material for electrochromic devices [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. The PEO-based electrolytes complexed with lithium salt and montmorillonite (MMT) nano-clay as filler have raised curiosity for research and development of solid-type novel PNCE materials for lithium batteries [1][2][3][4][5].…”

“…As compared to the solution-cast technique, the preparation of PNCE materials by melt compounded technique is more suitable for their large-scale technological applications, owing to its rapid, least expensive and dry procedure to prepare solvent free polymer electrolyte films [2,10,11,24]. The survey reveals that so far, the PNCE films of PEO-LiClO 4 -MMT composite have not been synthesized by direct melt compounded hot-press technique for the ion conduction characterization.…”